In recent years, a new micro-fabrication technology has been developed with the advances in the integration and in the performance of a semiconductor integrated circuit (LSI). In particular, there has been recently a progress in the movement to change a wiring material from a conventional aluminum (Al) alloy to copper (Cu) or Cu alloy (hereinafter, collectively referred to as Cu) with a low resistance in order to achieve the high-speed performance of the LSI. Since micro-fabrication of Cu is difficult with a dry etching method which is frequently used in forming an Al alloy wiring, a so-called damascene method is mainly employed for micro-fabrication of Cu. In this method, a Cu film is deposited on an insulating film on which a trench has been formed. Then, the portion of the Cu film, which is not buried in the trench, is removed with a chemical mechanical polishing (CMP) method. Thereby, a buried-Cu wiring is formed. In general, the Cu film is formed by firstly forming a thin seed layer with a sputtering method or the like, and then performing an electrolytic plating method thereon thus to form a stacked layer having a thickness on the order of several hundreds of nanometer (nm).